1. Field of the Invention
The present invention is generally related to equipment for cleaning steam generators and in particular to a high pressure fluid lance for cleaning sludge off the tubesheet and tubes by access to an open tube lane.
2. General Background
In nuclear power stations, steam generators such as recirculating steam generators (RSG's) are used for heat exchange purposes in the generation of steam for driving turbines. Primary fluid which is heated by the core of the nuclear reactor is lead through a collection or bundle of tubes in the RSG. A secondary fluid, generally water, which is fed into the space around the tubes receives heat from the tubes to provide a continuous steam generation cycle. Due to the constant high temperature and severe operating environment, a sludge mainly comprised of iron oxide such as magnetite builds up on the lower outer portion of the tubes and on the tube sheets that support the tube bundle. Since the sludge build up on the tube bundle and tube sheets reduces heat transfer efficiency and can cause corrosion, it is preferable that the tubes and tube sheets be cleaned periodically to remove the sludge.
Conventional RSG sludge lancing consists of the use of segmented lances, usually screwed together, that are moved into and out of the tube bundle by an externally mounted indexer. Operation of these lances requires that the lance sections be removed or added as the lances are retracted or advanced. The addition or removal of lance sections requires that the sludge lancing operation be stopped and it requires the presence of personnel in a radioactive area. Depending on the job and the number of passes required with the lance, as much as one half of the time scheduled for the operation involves adding and removing lance sections. This results in increased radiation exposure of personnel and unproductive down time of the nuclear steam supply system.
Patents related to sludge lancing-that applicants are aware of include the following.
U.S. Pat. No. 4,079,701 discloses a system for removing sludge from a steam generator wherein headers are arranged at the elevation of the sludge to be removed and a fluid lance is moved along the line between the headers.
U.S. Pat. No. 4,424,769 discloses an apparatus for the removal of sludge deposits on the tube sheet of a steam generator wherein a lance assembly is moved into and through the steam generator by a driving mechanism. Cleaning is carried out in successive sequences with different lances that direct cleaning fluid to the tube plate in different zones more and more remote from the lances.
U.S. Pat. No. 4,515,747 discloses a wheeled transporter that is pulled by cables along the tubesheet between the tube bundle and the steam generator shell. Inspection equipment or a nozzle for cleaning the tubesheet may be attached to the transporter.
U.S. Pat. No. 4,566,406 discloses a steam generator having a manifold with a plurality of nozzles for cleaning sludge from the tubesheet. The manifold is rigidly attached to the tubesheet and remains in place during normal operation of the steam generator.
U.S. Pat. No. 4,700,662 discloses a sludge lance wand for cleaning once through steam generators. A curved high pressure fluid feed tube has a plurality of feed tube extensions attached at one end and nozzles attached at a second end for directing fluid toward the tubesheet as the wand is moved through the steam generator.
U.S. Pat. No. 4,757,785 discloses a steam generator sludge removal apparatus wherein a track is assembled between the once through steam generator outer shell and circular shroud around the tube bundle. A motorized carriage driven on the track directs high pressure fluid toward the tube bundle through windows in the circular shroud.